As an electric power tool configured to drive a tip tool by an electric motor serving as a driving source, hammer, hammer drill, grinder and the like are known. Each of the hammer and the hammer drill has a drill bit, anchor drill and the like serving as a tip tool, and is also referred to as “impact tool”. These impact tools are used to cause the tip tool to apply an impact to a workpiece, or to rotate the tip tool while applying an impact to a workpiece. The grinder is an electric power tool for rotating a grinding wheel serving as the tip tool to grind a workpiece, and also referred to as “disc grinder” or “disc sander”. In addition, impact driver, impact wrench, and cutter are known as an electric power tools for driving a tip tool to machine a workpiece.
An electric power tool includes: an electric motor for driving a tip tool; and a motion converting mechanism for converting the rotation motion of a motor output shaft into rotation motion or impact-applying motion of the tip tool. For example, patent literature 1 discloses an impact tool working as an electric power tool which causes a tip tool to apply impact to a workpiece. According to this impact tool, a piston is reciprocably housed in a cylinder fitted with a tool holder, and an electric motor for driving the piston is incorporated in a housing.